Modeling fast biomass pyrolysis in a gas–solid vortex reactor Robert W. Ashcraft, Geraldine J. Heynderickx ⇑ , Guy B. Marin Ghent University, Laboratory for Chemical Technology, Krijgslaan 281, Building S5, Ghent B-9000, Belgium article info Article history: Available online 21 June 2012 Keywords: Multiphase CFD Flash pyrolysis Vortex Lignocellulosic Fluidized bed abstract Conversion of biomass via fast pyrolysis and other methods is positioned to be an important part of the energy landscape in the future. Pyrolysis of lignocellulosic biomass in a gas/solid vortex reactor (GSVR) is modeled to assess the potential of this centrifugal fluidization reactor technology and to explore its pro- cess intensification abilities. The production of pyrolysis gases, tar/liquids, and char/ash are examined for various operational scenarios using a simple reaction network. A brief comparison with traditional fluid- ization technologies is performed. The applied CFD model has been previously validated for non-reacting flows using experimental data from an in-house cold-flow apparatus. The product distribution from biomass pyrolysis between 450 and 500 °C was determined to be 14–17 wt.% char, 73–76 wt.% tar, and 8.5–9.5 wt.% pyrolysis gas, depending on the specific conditions of the process simulation, with all condi- tions yielding complete biomass conversion. The calculated convective gas/solid heat transfer coefficients in the GSVR were determined to be 650 W/(m 2 K), which is significantly larger than in non-rotating fluidization reactors. The GSVR exhibited the ability to intensify the biomass pyrolysis process with respect to both production per reactor volume and selectivity toward the desired products, indicating that further investigations with more detailed kinetics and/or experimental reactors is warranted. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The energy conversion and chemical process industries contin- uously strive to achieve more efficient, selective, and cost-effective processes, which is achieved through what is generally referred to as process intensification [1, 2]. This requires the implementation of new and disruptive technologies, such as new reactor types or process chemistry. The presented work focuses on a reactor type that has only recently been considered as a viable chemical reactor for traditional, high-volume industrial processes, such as petro- chemical and energy conversion applications. It can be described as a rotating bed reactor in a static geometry (RBR-SG) and can in- volve several different phase combinations. This paper will focus on a gas/solid RBR-SG, or gas/solid vortex reactor (GSVR), but many of the principles discussed will be applicable to other phase com- binations in a vortex-type reactor as well. Conversion of biomass, via fast pyrolysis and other methods, is positioned to be an important part of the energy landscape in the future. Pyrolysis of lignocellulosic biomass is particularly attractive because agricultural wastes and other non-food biomass sources can be utilized as the feedstock. Pyrolysis is one prospective bio- mass conversion technology that has the potential to produce gas- eous and liquid products that can be used in energy applications or in the production of high-value chemicals. Other potential energy conversion processes for lignocellulosic biomass include gasifica- tion, hydrothermal processing, and enzymatic/biological processing. Fast pyrolysis in traditional fluidization reactors, such as static fluidized beds (SFBs) and circulating fluidized beds or risers (CFBs), has been studied in recent years [3–9]. The reactor technology examined in the presented work is the gas/solid vortex reactor (GSVR), which harnesses centrifugal forces to enhance gas/solid heat and mass transfer. A schematic of a GSVR is provided in Fig. 1a. In a thorough review, Bridgwater and Peacocke outlined the three necessary characteristics of a fast pyrolysis process: (1) very high heating and heat transfer rates, (2) precise temperature control near 500 °C, and (3) rapid cooling of the pyrolysis vapors to prevent further cracking of the vapor-phase components [3]. The GSVR has the ability to meet all three criteria because of the high gas/solid slip velocities that result in high convective heat/ mass transfer coefficients and the very short gas-phase residence time in the reactor. In general, successful fast pyrolysis requires gas-phase residence times on the order of less than 0.2–2 s, depending on the intended application [3]. The GSVR naturally operates with conditions conducive to fast pyrolysis, which makes this technology a natural candidate for potential industrial implementation. In a GSVR, gas is injected tangentially into a cylindrical reactor chamber containing the solid-phase particles. Momentum is transferred from the gas to the particles, causing them to rotate in the chamber and generating a large centrifugal force. The large 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.06.048 ⇑ Corresponding author. Tel.: +32 (0)9 264 45 32; fax: +32 (0)9 264 49 99. E-mail address: geraldine.heynderickx@ugent.be (G.J. Heynderickx). Chemical Engineering Journal 207–208 (2012) 195–208 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej